AIDS is a pandemic disease that is having a significant socioeconomic impact on all levels of society in the 1990's. AIDS has already greatly affected the health delivery system in this country, with the number of diagnosed cases exceeding 160,000. Worldwide, the caseload is estimated to be 700,000 or more. For various reasons, few physicians are meeting the challenge of caring for HIV infected individuals. While some have a fear of contagion, many cite "a lack of knowledge about treatment of HIV" as their greatest deterrent for providing care. This expert Computer Assisted Instruction (CAI) system addresses the need for up-to-date treatment information and diagnostic techniques for detecting and correctly identifying the myriad of opportunistic infections (OI's) associated with HIV. The HIV-EXPERT computer system will assist physicians in becoming knowledgeable about the differential diagnosis of these OI's by utilizing a hierarchical knowledge base of information pertaining to these infections. This data base will be developed by medical experts in infectious disease and AIDS clinical care. Using heuristic rules with this knowledge base, the expert system will guide physicians through the maze of symptoms, laboratory tests, and diagnostic procedures to arrive at a correct diagnosis and a correct treatment plan.